dander n.1

"scurf which forms on the scalp or skin of the head and comes off in small scales or dust," 1540s; the first element is obscure (despite much speculation, OED concludes "nothing satisfactory has been suggested"). The second element probably is Northumbrian or East Anglian dialectal huff, hurf "scab," from Old Norse hrufa, from Proto-Germanic *hreufaz, source of Old English hreofla "leper." Middle English words for it were bran (late 14c.), furfur (c. 1400, from Latin), scales (mid-15c.).

"superfluous, exceeding what is natural or necessary," c. 1600, from Latin redundantem (nominative redundans), present participle of redundare, literally "overflow, pour over; be over-full;" figuratively "be in excess," from re- "again" (see re-) + undare "rise in waves," from unda "a wave" (from PIE *unda-, nasalized form of root *wed- (1) "water; wet").

Also sometimes in 17c. in a more positive sense, "abounding to excess or fullness, exuberant, plentiful," e.g. in "Paradise Lost," though what he meant by it here is anyone's guess:

With burnished neck of verdant gold, erect

Amidst his circling spires that on the grass

Floated redundant.

 Of persons, in employment situations by 1928, chiefly British. Related: Redundantly. As a verb, redund has been tried at least once (1904); the etymological corresponding verb is the Frenchified redound.